It has been known for many years to coat small particles, such as seeds and pharmaceutical products. Generally, a coating which increases the weight of the seed up to 25% is defined as a film coating. A coating which increases the weight of the seed more than 25% is referred to as pelletizing. Pelletizing provides uniformity of size to the particles. Depending on the extent of coating applied, pelletizing may provide a spherical shape to the particles which are normally elongated or irregularly shaped.
There are three primary reasons for providing a coating to such particles. First, a protective coating is often applied to seeds so as to prevent dust-off of prior treatments that have been applied. For example, a film of biological material may be applied to the seed to increase the viability of the seed, and a protective coating is needed to prevent the film from being worn away from the seed during handling. The protective coating allows for a reduction in the amount of film treatment that needs to be applied, thus reducing costs to the seed company. The protective coating also increases the effectiveness of the film treatment by encapsulating the film on the seed. Also, the protective coating reduces environmental hazards of the film treatment.
Another purpose of providing a coating to seeds and small pharmaceutical products is to increase the size of the particle. Particularly for seeds which are too small to be mechanically planted, such an increase in size allows small seeds to be planted mechanically, rather than manually, thereby resulting in significant labor savings, both during the planting and by eliminating manual thinning. Mechanical planting also reduces the seed population required for planting, thereby providing further cost savings.
A third benefit provided by seed coatings is to increase the visibility of the seeds during planting. Therefore, more accurate and less wasteful planting results.
In prior art pelletizing operations, a binder material in a solution was applied by spray, and then a bulking agent, such as clay or wood fibers, was manually applied to the seeds. After the two-step binding and bulking operations were completed, the coated seeds were then taken to an oven to bake dry. Thus, the prior art multiple-step process was slow, time consuming, and labor intensive.
Therefore, a primary objective of the present invention is the provision of an improved method and means for continuously coating particulate material, such as seeds.
Another objective of the present invention is the provision of a method and means for continuously coating seeds, wherein the coating solution is applied and dried in a rotating drum.
A further objective of the present invention is the provision of a method and means for coating seeds wherein multiple layers of different coatings can be applied to the seeds in a continuous process.
Still another objective of the present invention is the provision of a method and means for continuously coating seeds in a rotating drum having high air flow through the drum so as to maintain low drying temperatures.
A further objective of the present invention is the provision of a method and means for continuously pelletizing seeds wherein a binder and a bulking agent are applied simultaneously in a solution.
Yet another objective of the present invention is the provision of a continuous pelletizing machine having a tilted rotatable drum which is vented for substantially instantaneous drying of the seeds as the seeds are coated.
Still another objective of the present invention is the provision of a method and means for continuously coating particulate material wherein the flow rate of the material through a drum is selectively adjustable.
Yet another objective of the present invention is the provision of a method and means for coating particulate material in a rotating drum which is maintained at a negative pressure.
A further objective of the present invention is the provision of a means for continuously coating particulate material which is economical to manufacture, and efficient and durable in use.
These and other objectives will become apparent from the following description of the invention.